Millions of Facebook users may be getting too open with their personal information on the Web's biggest social network.

According to Consumer Reports, an estimated 13 million Facebook users in the United States either do not use or are not aware of the site's privacy controls. In addition, 28 percent of the people the magazine polled said they share either all or almost all of their Facebook posts with people beyond their "friends." In addition, only 37 percent of users say they have used the site’s privacy tools to limit how much information apps are allowed to see.

"Facebook really ischanging the way the world socially communicates and has become a successful service in part by leveraging copious amounts of personal data that can be spread far wider than its users might realize," said Jeff Fox, Consumer Reports Technology Editor, in a statement.